A small-signal voltage V(t)=Vo sinωt is applied across an ideal capacitor C 
  • over a full cycle, the capacitor C does not consume any energy from the voltage source

  • current I(t) is in phase with voltage V(t)

  • current I(t) leads voltage V(t) by 180°

  •  current I(t) lags voltage V(t) by 90°

An inductor 20 mH, a capacitor 50μF, and a resistor 40Ω are connected in series across a source of emf V=10sin340t. The power loss in the AC circuit is:

  • 0.67 W

  • 0.78W

  • 0.89 W

  • 0.46 W

A resistance 'R' draws power 'P' when connected to an AC source. If an inductance is now placed in series with the resistance, such that the impedance of the circuit becomes 'Z' the power drawn will be:
1. PRZ22. PRZ3. PRZ4. P 
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A series R-C circuit is connected to an alternating voltage source. Consider two situations:

1. When the capacitor is air-filled.

2. When the capacitor is mica filled.

Current through the resistor is I and voltage across the capacitor is V then
  • Va<Vb

  • Va>Vb

  • ia>ib

  • Va=Vb

A transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6A, the voltage across the secondary coil and the current in the primary coil respectively are
 

 

 
  • 300V,15A

  • 450V,15A

  • 450V,13.5A

  • 600V,15A

A coil of self-inductance L is connected in series with a bulb B and an AC source. The brightness of the bulb decreases when

  • frequency of the AC source is decreased 

  • the number of turns in the coil is reduced

  • a capacitance of reactance Xc=XL is included in the same circuit

  • an iron rod is inserted in the coil

In an electrical circuit R, L, C, and an AC voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and the current in the circuit is π/3. If instead, C is removed from the circuit, the phase difference is again π/3. The power factor of the circuit is

  • 1/2                                           

  • 1/2

  • 1                                             

  •  3/2

The instantaneous values of alternating

current and voltages in a circuit are given

as 

i=12sin(100πt) amperee=12sin(100πt+π/3) volt

The average power in Watts consumed in the

circuit is

  • () 14

  • () 34

  • () 12 

  • () 18

An AC voltage is applied to a resistance R and an inductor L in series. If R and the inductive reactance are both equal to 3Ω, the phase difference between the applied voltage and the current in the circuit is

  • π/4                                                

  • π/2
  • zero                                                
  • π/6

The rms value of potential difference V shown in the figure is

                        

  •  Vo                                                     

  •  Vo2

  • Vo2                                                     

  •  Vo3   

A coil has resistance 30 Ω and inductive reactance 20 Ω at 50 Hz frequency. If an AC source of 200 V, 100 Hz, is connected across the coil, the current in the coil will be:

  •   4.0 A                                           

  •   8.0 A

  •   2013A                                         

  •   2.0 A

A 220V input is supplied to a transformer.The output circuit draws a current of 2.0A at 440V. If the efficiency of the transformer is 80%, the current drawn by the primary windings of the transformer is 

  • 3.6A                                       

  • 2.8A

  • 2.5A                                       

  • 5.0A

Power dissipated in an L-C-R series circuit connected to an AC source of emf ε is 

  • () ε2RR2+Lω-1Cω2

  • () ε2R2+Lω-1Cω2R

  • () ε2R2+Lω-1Cω2R

  • () ε2RR2+Lω-1Cω2

 

In AC circuit the emf (e) and the current (i) at any instant are given respectively by

e=Eo sin ωt

i=Iosin (ωt-ϕ)

The average power in the circuit over one cycle of AC is 

 

  • EoIo2

  •  EoIo2sin ϕ

  •  EoIo2cos ϕ

  •  EoIo

In an ideal transformer, the voltage and the current in the primary are 200 volt and 2 amp. respectively. If the voltage in the secondary is 2000 volt. Then value of current in the secondary will be – 

  •   0.2 amp.                     

  •   2 amp. 

  •   10 amp.                       

  •   20 amp.

An inductor 20mH, a capacitor 50μF, and a resistor 40Ω are connected in series across a source of emf V = 10sin340t. The power loss in the AC circuit is:
  • 0.67 W
  • 0.76 W
  • 0.89 W
  • 0.51 W

A resistance ' R' draws power 'P' when connected to an AC source. If an inductance is now placed in series with the resistance, such that the impedance of the circuit becomes 'Z' the power drawn will be

  • \(P\Big({\large\frac{R}{Z}}\Big)^2\)

  • \(P\sqrt{\large\frac{R}{Z}}\)

  • \(P\Big({\large\frac{R}{Z}}\Big)\)

  • \(P\)

In an AC circuit an alternating voltage e=2002sin100t volt is connected to a capacitor of capacity 1μF. The RMS value of the current in the circuit is:

  •   100 mA

  •   200 mA

  •   20 mA

  •   10 mA

In the given circuit, the reading of voltmeter V1 and V2 are 300 V each. The reading of the voltmeter V3 and ammeter A are respectively:

  • 150 V, 2.2 A

  • 220 V, 2.2 A

  • 220 V, 2.0 A

  • 100 V, 2.0 A

Power dissipated in an L-C-R series circuit connected to an AC source of emf E is:
  • \(\frac{\varepsilon^2R}{\Big[R^2+\Big(L\omega-\frac{1}{C\omega}\Big)^2\Big]}\)
  • \(\frac{\varepsilon^2\sqrt{R^2+\Big(L\omega-\frac{1}{C\omega}\Big)^2}}{R}~\)
  • \(\frac{\varepsilon^2\Big[R^2+\Big(L\omega-\frac{1}{C\omega}\Big)^2\Big]}{R}\)
  • \(\frac{\varepsilon^2R}{\sqrt{R^2+\Big(L\omega-\frac{1}{C\omega}\Big)^2}}~\)

What is the value of inductance L for which the current is a maximum in a series LCR circuit with C = 10 μF and ω=1000 s-1?

  • 100 mH

  • 1 mH

  • cannot be calculated unless R is known

  • 10 mH

A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately :

  • 30%

  • 50%

  • 90%

  • 10%

A transistor-oscillator using a resonant circuit with an inductance L (of negligible resistance) and a capacitance C has a frequency f. If L is doubled and C is changed to 4C, the frequency will be:

  • f/4

  • 8f

  •  f/22

  • f/2

The core of a transformer is laminated because :

  • the weight of the transformer may be reduced

  • rusting of the core may be prevented

  • ratio of voltage in primary and secondary may be increased

  • energy losses due to eddy currents may be minimized

A coil of inductive reactance 31 Ω has a resistance of 8 Ω. It is placed in series with a condenser of capacitive reactance 25 Ω. The combination is connected to an a.c. source of 110 V. The power factor of the circuit is:

  • 0.56

  • 0.64

  • 0.80

  • 0.33

The variation of EMF with time for four types of generators is shown in the figures. Which amongst them can be called AC?

  • (a) and (d)

  • (a), (b), (c), (d)

  • (a) and (b)

  • only (a)

A circuit when connected to an AC source of 12 V gives a current of 0.2 A. The same circuit when connected to a DC source of 12 V, gives a current of 0.4 A. The circuit is:

  • series LR

  • series RC

  • series LC

  • series LCR

For the circuit shown in the figure, the time constant is

1. 1011s2. 910s3. 57s4. 34s
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If i=2t, then the R.M.S. value of current between 0 to 2 second is

1. 232. 433. 534. zero 
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L, C, and R denote inductance, capacitance, and resistance respectively. pick out the combination which does not have the dimension of frequency.

1. 1RC2. RL3. 1Lc4. CL
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0:0:1


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